It's either a contractual thing or a legal thing. Note that there are multiple countries with this restriction:
Oanda - Leading Forex / CFD broker* with direct Zorro connection, free historical price data, and no minimum lot size. Click the link to open an account (not for US, Canada, Australia, France, Belgium, Netherlands, Poland, Hong Kong, Singapore, and Japan residents). After the first trade, contact support@opgroup.de for your free Zorro S subscription.
I suspect a lot of countries' politicians want to protect their citizens from predatory free candy, like professional trading software.
